1. Field of the Invention
This invention relates to a vehicular drive system including a mechanical type power transmitting portion having a plurality of coupling elements, disposed between a power drive source and drive wheels, which are combined in operation to change a rotation speed of a drive power being output from the drive power source. More particularly, it relates to a control device for a vehicular drive system that can suitably determine a rotation direction of an output shaft of the mechanical type power transmitting portion without increasing the number of component parts.
2. Description of the Related Art
A vehicular drive system has heretofore been well known as including a mechanical type power transmitting portion having a plurality of coupling elements, disposed between a power drive source and drive wheels, which are combined in operation to change i.e., alter a rotation speed of a drive power being output from a drive power source
For instance, Patent Publication 1 (Japanese Patent Application Publication No. 2005-264762) discloses a vehicular drive system of such a structure described above. With the control device of such a vehicular drive system, the mechanical type power transmitting portion includes a step-variable type automatic transmission. An overall speed ratio (total speed ratio) of a whole of the drive system is established with a speed ratio of an electrically controlled differential portion, rendered operative to function as a continuously variable transmission, and a speed ratio corresponding to each gear position (shifting position) of the mechanical type power transmitting portion. Further, with the structure disclosed in Patent Publication 1, the control device includes a rotation speed sensor for detecting a rotation speed, corresponding to a vehicle speed, of an output shaft of the mechanical type power transmitting portion.
Besides the foregoing, various technologies have heretofore been known as disclosed in Patent Publication 2 (Japanese Patent Application Publication No. 2001-339805), Patent Publication 3 (Japanese Patent Application Publication No. 8-183356), Patent Publication 4 (Japanese Patent Application Publication No. 2002-281607), Patent Publication 5 (Japanese Patent Application Publication No. 9-37410), Patent Publication 6 (Japanese Patent Application Publication No. 9-98516), Patent Publication 7 (Japanese Patent Application Publication No. 2000-238555) and Patent Publication 8 (Japanese Patent Application Publication No. 2000-197208).
Meanwhile, with the control device for the vehicular drive system disclosed in Patent Publication 1 and other Patent Publications, the rotation direction of the output shaft is determined based on a rotational direction signal detected by a resolver that can detect a rotation speed and rotation direction of, for instance, a second electric motor. In particular, under a circumstance where with the second electric motor and mechanical type power transmitting portion placed in an operatively interlocking state, i.e., in a power transmitting state, the shifting position of the mechanical type power transmitting portion is selected in a forward running gear position like a 1st-speed gear position, the second electric motor and output shaft of the mechanical type power transmitting portion rotate in the same the rotation direction.
In contrast, under a situation where the shifting position of the mechanical type power transmitting portion is selected in a reverse running shift position, the second electric motor and output shaft rotate in rotation directions opposite to each other. Detecting the rotation direction of the second electric motor based on such consequences allows the rotation direction of the output shaft of the mechanical type power transmitting portion to be determined.
However, with the power transmitting path between the second electric motor and mechanical type power transmitting portion placed in an interruptive state, i.e., a neutral condition, the second electric motor and output shaft of the mechanical type power transmitting portion are interrupted in operation. This makes it impossible to determine the rotation direction of the output shaft. Thus, the rotation direction of the output shaft becomes indeterminate. This results in incapability of deciding the magnitude of demanded drive power when the shift position is shifted in a drive position. Thus, a research and development work has been needed to provide a method of determining the rotation direction.
Likewise, a research and development work has been needed to provide a method of determining the rotation direction of the output shaft with high precision even in a drive mode or in a switching mode wherein the power transmitting path is switched from a power cut-off state to a power transmitting state.
The single rotation speed sensor of the related art, disposed on the output shaft, has a capability of detecting the rotation speed but has encountered a difficulty of detecting even the rotation direction of the output shaft. The rotation speed sensor of the related art is mounted in a position closer to an area formed with a convexed and concaved surface like a toothed surface of a gear integrally rotatable with, for instance, the output shaft of the mechanical type power transmitting portion. A variation occurring in distance between the convexed and concaved surface and the rotation speed sensor allows a signal current, caused in a coil of the rotation speed sensor, to be detected. Converting a variation in such a signal current to a voltage allows a pulse to be formed with a speed of such a variation in pulse being detected in conversion to a speed.
Thus, the formation of such a pulse enables the detection of the rotation speed but it is impossible to detect even the rotation direction. On the contrary, a plurality of rotation speed sensors may be equipped to enables the detection of the rotation direction. However, this results in the occurrence of an issue with an increase in the number of component parts with a resultant increase in production cost and an increase in size of the drive system due to an additional number of the rotation speed sensor.